US 2399018 A
Description (OCR text may contain errors)
April 23, 1946.
G. GREENSLADE TESTING DEVICE Filed Jan. '19, 1943 4 Sheet-Sheet 1 swam kw Grove-11R. G'reenslade A ril 23, 1946. e. R. GREENSLADE 2,399,018
TESTING DEVICE Filed Jan. 19, 1945 4 Sheets-Sheet 2 1E NR INVENTOR 'G'rar erli". G're enslade April 23, 194 6. a. R. GREENSLADE TESTING DEVIbE Filed Jan. 19, 1943 4 Sheets-Sheet 3 Grover 1?. GreensZad e April 23, 1946 fi 7. I
G. R. GREENSLADE TESTING DEVICE 4 Sheets-Sheet 4 age) 62 Graverli'. Greenslade Patented Apr. 23,1946
TESTING DEVICE syiva Application January 19, 1943, Serial No. 472.84%
Claims. (01. 175-183) This invention relates to the testing of hollow or tubular articles of electrically conducting material and, in particular, to the testing of such articles for the presence of hidden flaws or defects such as partial transverse fractures or the like.
Numerous hollow or tubular articles of metal are subjected to heavy stresses in service and it is highly important to know when such articles have defects which might make further use thereof a hazard to property and life. As example, hollow axles for railway rolling stock and particularly locomotives, locomotive crank pins and boiler staybolts may be mentioned. While various forms of testing devices have been proposed heretofore for such articles, the present invention utilizes a novel principle of operation and is highly effective in revealing the presence of dangerous defects in hollow metal articles.
In a preferred embodiment of the invention, I provide a testing device adapted to be inserted into the article to be tested. The device has spaced contacts projecting laterally therefrom adapted to engage the interior of the article and make electrical contact therewith. The device of my invention also includes a resistance element and resistor coils adapted to constitute a Wheatstone bridge with the portion of the article being tested between the contact points of the device as one of the'iour sides of the bridge. The testing device also includes a self-contained current source and a galvanometer. When the device has been initially inserted in the article to showing it in position within a hollow or tubular metal article to be tested;
Figure 3 is a transverse section'through the device taken along the plane of line III-III of Figure 2;
Figure 4 is a diagram showing the circuit which the various parts of the device are connected to form a Wheatstone bridge with a portion of the article being tested as the fourth arm thereof;
Figure 5 is an end elevation of a modified form of device;
Figure 6 is a longitudinal section therethrough taken along the plane of line VI-VI of Figure 5, showing the device in position within an article to be tested;-
Figure 7 is a longitudinal sectional view through a further modified form of testing device showing it in position within an article to be tested: and
be tested, the bridge is balanced and the device is then caused to traverse the length of the interior of the article so that the contacts thereof engage the article at a succession of equally spaced points along the interior thereof. Since the resistance of the portion of the article between the contact points is increased upon the occurrence of a defect such as a transverse fracture therein, a definite indication on the galvanometer will be observed when the contact points embrace any such defect therebetween.
A more complete explanation of the device and its operation will be given during the following detailed description which refers to the accompanying drawings illustrating apreferred embodiment. In the drawings:
Figure 1 is a partial longitudinal section through the device'of my invention with parts in elevation and parts shown diagrammatically;
Figure 2 is a partial longitudinal section throughthe forward end of the testing device Figure 8 is a simplified diagram illustrating how the circuits shown in Figure 7 form a Wheatstone bridge with a portion of the article being tested as the fourth arm.
Referring now in detail to the drawings and, for the present, to-Figures 1 through 4, a testing device embodying my invention indicated generally at l0 comprises a tubular body or casing II having a removable closure I2 at its rear or handle end. The device II! is of such size as to be readily insertible within the hollow or tubular articles to be tested. A disc ii of insulation disposed transversely in the casing l l and secured therein by screws It provides a chamber in the handle end of the device for a dry cell l5. A contact rivet 16 in the disc i3 is adapted to be engaged by the central terminal of the cell. The closure It" has a conducting ring I! thereinseparated by insulation from the closure itself. A spring I8 engaging the ring I! holds the cell with its central terminal in contact with the rivet It. A conductingstrip i9 suitably insulated is secured to the ring ll and extends upward through the cell chamber between the cell and the casing H to a terminal screw 20.
A control switch for the cell i5 is provided by a relatively fixed contact finger 2i held in place by the rivet l6 and a movable finger 22 secured to the disc l3 by a rivet 23. A push button 24 mounted in the wall of the casing ll serves, when pressed, to actuate the finger 22 into engagement with the finger 2 I. a
Resistor coils 25 and 26 are non-inductively wound on a spool 21 of insulation mounted on brackets 28 secured to the interior of the casing a shaft 32 extending radially through the wall of the casing and having a suitable operating knob (not shown) on the exterior thereof. A galvanometer 33 is mounted on the exterior of the de-- vice and the wall of the casing II is provided with an opening 34 for leads connected to the galvanometer.
A resistor element 35 in the form of a block of conducting metal is mounted in the forward end of the device being secured to the casing H by screws 35 but insulated therefrom. The element 35 is preferably a block of steel if the members to be tested are predominantly of that metal as will usually be the case. Holes 31 near the ends of the block 35 are each provided with a pair contact points. The hole 31 nearer the forward end of the device has contacts 35 and 33 therein adapted to engage, respectively, the interior of an article to be tested shown at 45 and the bottom of the hole 31. A spring 4| normally tends to urge the contact points apart and into engagement with the surfaces just mentioned. An insulating bushing and washer separate the contact 33 from the casing I and a bushing. similarly prevents engagement of the contact 33 with the block 35 except at the extremity of the former. The contact points 38 and 33 are connected by a slack wire Jumper 42.
The hole 31 in the block 35 remote from the forward end of the device is similarly provided with contact points 43 and 44. A disc of insulation separates the spring 4| from the contact point 44. By virtue of the construction described, it will be apparent that the contact points 35 nd 43 are adapted to have yielding engagement with the interior of the article 40 when the device I0 is inserted therein.
Figure 4 illustrates the circuit in which the various parts of the device are connected. The connecting leads have been omitted from Figures 1 and 2, for the sake of clear'ness. It will be apparent that in the circuit of Figure 4, the coil 25 forms one side of a Wheatstone bridge while the coil 25 plus the variable resistor 29 forms another side. The block 35 forms still another side and the contacts 33 and 43 are so connected that the portion of the article 40 'therebetween constitutes the fourth side. It is evident that the circuit will be energized from the cell I5 on actuation of the push button 24. Thus when the device l0 has been initially inserted into the article to be tested, the bridge may be balanced by adjusting the resistor 29 so that the galvanometer 33 shows 'no deflection. When this has been done. the testing device is moved bodily along the article with the contact points 35 and 43 in constant engagement with the interior thereof. Should the article have a defect therein-such as a transverse fracture which would afiect the electrical resistance of the neighboring portion of the length of the article, this will be immediately indicated by an unbalancing of the bridge when the contact points 38 and 43 are on opposite sides of the fracture. A definite indication is thus obtained of the presence-of any defect or flaw such as a fracture which would increase the resistance of the article when measured longitudinally. The resistance of the block 35 is preferably of the same general order as the resistance of that portion of the article between points 35 and 43.
Figure 2 illustrates how the leads are connected to thecontact points 33, 33, 43 and 44. To permit such connections, holes 45 are drilled into the block 35 and through the insulating bushings, intersecting the holes 31.
Figures 5 and 6 illustrate a modified form of device which is generally similar to that already described and the corresponding parts thereof are designated by similar reference numbers with a prime attached. The principal difference between the two modifications is in the shape of the resistor elements 35 and 35'. The latter is shaped to extend across the full diameter of the casing It. A further change is the location of contacts 43' and 44' diametrically opposite from the points 38' and 35'. This permits the device to reveal the presence of a defect regardless of its angular location about the axis of the bore through the article being tested. The device of Figures 1 through 3, obviously, will reveal the presence only of defects which are more or less in alignment with the positions of the contact points. This is advantageous where it is desirable to locate the angular relation of the defect as well as its position along the length of the article being tested. While an article may be completely tested with the device of Figures 1 through 3 by making several passes of the device through the article in different angular relations, the device of Figures 5 and 6 will reveal any defect, regardless of its location about the axis of the bore, on a single pass of the device through the article. The mode of manipulation of the modified device and the functioning thereof are the same as have already been described with reference to Figures 1 through-l. In both forms of the invention, the use of contact points engaging the resistor element compensates for the contact resistance between the article being tested and the contact points engaging therewith. This eliminates errors which might otherwise be mistaken for indications of defects.
Figure '7 illustrates a further modified form of testing device indicated generally at 55. This form of device comprises a resistor block 5| having contact points 52 and 53 secured thereto, the former being in contact with the block and the latter being insulated therefrom by a bushing 54. The block 5| is pivotally mounted in a yoke 55 having a handle formed thereon. A leaf spring 55 secured to the block by a shackle 51 is adapted to engage the interior of the article being tested indicated at 58 on one side and urge the points 52 and 53 into engagement with the article on the other side of the interior thereof. A variable resistor 59, a fixed resistor 60 and a galvanometer 5| are connected in the form of a Wheatstone bridge, as shown in Figure 8, with the element 5| as the third arm and the portion of the article 53 between the points 52 and 53 as the fourth arm. The resistors 59 and 50 and the eaivanometer 5| may conveniently be mounted in a suitable case and connected by flexible leads, as shown, to the block 5| and points 52 and 53. The case for the resistors and galvanometer may also include a current source such as a dry cell 52.
Figure I shows the actual circuit connections but Figure 8 shows a schematic diagram thereof from which the existence of the Wheatstone bridge may be more readily observed, corresponding parts being similarly numbered in both figures. It will be noted that contact point 52 at the positive terminal of the dry cell 82 in both' figures and that leads from the resistor 60 and galvanometer 6| are connected to the other end of the block Similarly, the contact point 53 makes connection to the interior of the article 58 for leads from the resistor 59 and the galvanometer 6i. It will thus be apparent that the resistors 59 and 60 form two adjacent arms of the bridge while the block 5| forms the third arm and the portion of the article between contact points 52 and 53 constitutes the fourth arm. with this explanation, it will be understood that the device of Figure 7 functions in the same manner as those already described to produce an indication on the galvanometer when the portion of the article being tested embraced between the contact points has a defect therein such as to I an improved device for testing tubular or hollow articles of electrically conducting'material such as metal. The accuracyof the Wheatstone bridge for resistance measurement is well understood and the device of my invention applies its high sensitivity to the testing of hollow articles with the result that even exceedingly small flaws or fractures may be detected before they reach such proportions as dangerously to impair the strength of the articles wherein they occur.
Although I have illustrated and described but a few forms of the invention, it will be recognized that changes in the construction and arrangement of the parts may be made without departing from the spirit of the invention or the scope of the appended claims.
1. A testing device for articles composed of electrically conducting material comprising a member adapted to be disposed in cooperative relation with the article, a pair of contacts projecting from said member adapted to engage spaced points on the article when in such relation thereto, a conducting block secured to said member having a resistance or the same general order as the portion of the article between said contacts, a second pair of contacts similar to the first-mentioned contacts spaced along and engaging said block, yielding means urging said first-mentioned contacts outwardly from said member for engagement with the article and said second-mentioned to the ends of the third side of the bridge, said second-mentioned pair of contacts being connected to the ends of the remaining side of the bridge, a galvanometer on said member con'- nected between two opposite corners of the bridge and connections from the remaining corners of the bridge to a current source.
3. A device for testing hollow articles of electrically conducting material comprising a member adapted to be inserted into said articles, contacts spaced along said member, projecting therefrom and adapted to engage the interior of the articles when said member is inserted therein, a conducting block secured to said member but insulated therefrom, a second pair of contacts similar to the first-mentioned contacts spaced along and engaging said block, yielding means urging said first-mentioned contacts outwardly from said member for engagement with the article and said second-mentioned contacts against said block under substantially the same pressure, a pair of resistors adjacent said member, one of said resistors including a variable portion, said resistors being connected to form adjacent sides of a Wheatstone bridge, said first-mentioned contacts being connected to the ends of the third side of the bridge, said second-mentioned contacts being connected to the ends of the remaining side of the bridge, a galvanometer on said member connected between two opposite corners of the bridge, and connections from the remaining corners of the bridge to a current source.
the same order as that portion of the article bea tween said contacts, a second pair of contacts similar to the first-mentioned contacts carried by and engaging said member, common means for urging one contact of the first pair outwardly of said member and one contact of the second pair against said member, similar means for urging the remaining contacts outwardly of and against the member, respectively, a pair of resistors including a variable portion, said resistors being connected to form adjacent sides of a Wheatstone bridge, said first-mentioned contacts being connected to the ends of the third side of the bridge, said second-mentioned contacts being connected to the ends oi'the remaining side of the bridge, a galvanometer connected between two opposite corners of the bridge and connections from the remaining corners of the bridge to a current source.
5. A testing device as defined by claim 4 characterized by said means comprising back-up springs each engaging one of said first-mentioned pair of contacts and one of said second pair of contacts, whereby the contact resistance between saidmember and said second pair of contacts compensates substantially for the resistance between the first-mentioned pair of contacts and the article.
GROVER R. GREENSLADE.